This invention involves both the field of agricultural oil refining and the field of nutrient material manufacture.
Vegetable oils are natural fats which occur in the seeds of oil-seed plants such as soybean, cotton, corn and sunflower. Other agricultural oils are fish oils, animal fats and mixed vegetable-fish-fats.
The oils are solvent extracted and refined for edible use as cooking oil (e.g., Wesson Oil(trademark)), shortening (e.g., Crisco(trademark)), salad dressings, mayonnaise and margarines.
Agricultural oil refining essentially involves the removal of free fatty acids (FFA) and gums (to a lesser extent) form the crude oil. Gum removal is sometimes facilitated by addition of traces of phosphoric acid. The refining is accomplished by mixing the oil with a hot, aqueous caustic solution (sodium hydroxide) and centrifugally separating the reaction products from the xe2x80x9crefinedxe2x80x9d oil. The waste product, an alkaline mixture of saponified FFA and gums is referred to as soapstock.
The soapstock waste has commercial value, because of the fatty acid content as a high energy feed supplement, but must be processed further in order to render it salable. Processing simply amounts to breaking or splitting the soap into oil and water again by adding acid (Sulfuric acid) to approximately pH 1.5. After heating and mixing thoroughly, the acidulated soapstock is allowed to settle out. The oil that floats to the top is called xe2x80x9cacid oilxe2x80x9d and is drawn off for sale usually as an animal feed supplement. The aqueous phase remaining is termed xe2x80x9cacid waterxe2x80x9d. Acid water is the final waste product and is discarded. However, there is a disposal problem. Acid water contains all the undesirable and objectionable pollutants of the refining process. Sewer authorities at a bare minimum require that the acid water be neutralized (NaOH is added) before the waste is allowed to be dumped. Some states have more stringent pollution control and have forced companies out of business because of acid water disposal.
Thus, in the conventional refining of agricultural oils, sodium hydroxide is used as the refining base, sulfuric acid used to acidulate soapstock and sodium hydroxide again employed to neutralize acid water.
Although established and inexpensive, this technology results in a waste product that, due to environmental legislation, has become increasingly difficult and costly to dispose of.
Furthermore, in conventional sodium hydroxide refining the refined oil which exits the centrifuge or separator must be processed through a number of water wash unit operations in order to remove any water soluble components from the refined oil. These water wash steps, in which water is mixed into the oil and then separated from the oil, produce a waste water stream with extremely low levels of water soluble components.
Moreover, it has been found that sodium hydroxide refining does not always result in an optimum degree of clarity in the refined oil.
Also, the sodium hydroxide process does not maximize the amount of refined oil recovered from a given amount of crude substrate. At the same time, the sodium hydroxide process has not been found to minimize the amount of oil lost to the soapstock where it adds to the volume of what is normally a waste stream with disposal costs associated with it.
Also, the sodium hydroxide process is found to have significant problems with an xe2x80x9cinterlayerxe2x80x9d or xe2x80x9cgumxe2x80x99 which creates purification problems (degumming) because the amount of the interlayer tends to reduce the amount and purity of the desired refined oil.
Furthermore, the sodium hydroxide process does not appear to maximize the separation of refined oil from soapstock. The value of the soap can be more readily realized when it is part of the soapstock stream rather than representing trace impurities in the refined oil stream.
Also, the soapstock from the conventional sodium hydroxide process possesses less than optimal viscosity, depending on the concentration, causing difficulties in handling and transport, especially when refining and acidulation are conducted significant distance apart. It is then necessary to load the soapstock into railroad tank cars, tank trucks or barges, at which point that viscosity of the soapstock complicates and increases the cost of transport.
Since all of chemicals used to refine, acidulate and neutralize together with the undesirable constituents of crude oil, gums etc., are found in concentrated form in the acid water, examination of acid water will show it to be high in BOD, soluble salts and phosphorus. The soluble salts are primarily sodium sulfate and sodium phosphate. The sodium comes from the refining base (NaOH) and the acid water neutralizer (NaOH); the sulfate from the acidulating acid (H2SO4); the phosphorus from naturally occurring phosphatides (gums), which are hydrolyzed during acidulation into phosphate, and pretreat or process additions of phosphoric acid. Plant protein and carbohydrate fragments together with glycerol and residual oil produce the high BOD levels.
Enactment of environmental legislation has caused the disposition of soapstock and, in particular, acid water to become an increasingly difficult and costly problem. Not only is acid water highly acidic, it is high in b.o.d. and phosphorus. Several localities have strict effluent standards which force refiners to ship soapstock to an area with more liberal regulation where it can be acidulated.
In 1982 a privately funded research program was initiated to attempt to discover novel treatment processes for a large volume industrial waste product, the disposal of which had gained the attention of the Environmental Protection Agency (E.P.A.).
Phosphorus, the main component of the industrial waste, was creating a pollution problem which gained national and international attentionxe2x80x94the eutrophication of a valuable natural resource, rivers and lakes. The E.P.A. focused on the problem and many plants/businesses were forced to close for non-compliance with the Federal Water pollution Control Act (Clean Water Act) of 1972 and amendments of 1977 and 1981.
Additional emphasis was placed on the waterways of the Great Lakes Basin area of the U.S. and Canada. The Great Lakes Water Quality Agreement of 1978 was signed and the International Joint Commission was established by the United States and Canada. The new Agreement reinforces the importance of controlling phosphorus pollution. The importance of this continuing effort to enforce stricter standards is of special concern, since the Great Lakes region has one of the highest densities of industries that generate the waste product in the world.
At present, there is no treatment technology available to industry that will meet proposed E.P.A. standards.
According to a recent statement by W. R. Grace Company:
xe2x80x9cIn an effort to address the environmental concerns that this industry faces, W. R. Grace is pioneering a new refining technology-Modified Caustic Refining (MCR). MCR utilizes TriSyl""s ability to adsorb significant quantities of phophatides and soap, thereby eliminating the need for the water wash centrifuge step. Elimination of this unit operation results in lower wastewater treatment cost, and improved adsorbent utilization.xe2x80x9d
This demonstrates the importance of environmental concerns that the vegetable oil industry is facing.
W. R. Grace is promoting a method that reduces the remaining soap and phosphatides from once refined oil that previously was removed by a water wash, which shows that the industry struggles to find a cost efficient technology or method, or am technology, that prevents or minimizes the residual amounts of soap and phosphatides from the environment.
A recent issue of Water Pollution Control Facilitates magazine further indicates the general doctrine of water pollution control: that the so-called xe2x80x9cnutrientsxe2x80x9d (nutrients apparently relate to the extent that the component causes undesirable plant growth in waste water streams) is an undesirable nuisance which must be removed from the waste water stream using sophisticated separation techniques. This feeling in the pollution control art probably derives from the fact that the fundamental doctrine of those now working in the waste water field is that waste water is something that is supposed to be ejected from the system. This narrow-minded doctrine probably derives from the inbred historical paranoia in western civilization concerning waste water.
Nutrient Industry
The horticulture industry and hydroponic-growing represent one of the fastest growing areas of the agricultural market. In 1980 the USDA Crop-Reporting Board showed that foliage production was up 11% from 1979. In 1981 the USDA reported a 7% increase in the wholesale value of all sales of floriculture crops to $1,020,000,000.
As the horticulture market expands, so does the demand for high-grade fertilizer. The potential for continuing the growth is indeed impressive. A comparison of the American and European consumer buying habits shows that Europeans buy 10.1 fresh flowers and plants per capita against only 1.9 in the United States. The differential is strikingly similar to the american-European wine consumption pattern that existed only 10-15 years ago. As the horticulture industry becomes more mass-merchandise oriented and steps up its promotional efforts to take advantage of the potentials, the demand for fresh flowers and plants will be enormous.
The greenhouse-grown plant industry represents the technological leading edge of agricultural science and business. Computers select which crops should be grown and control water and nutrient flows. Genetically-engineered seeds and plants are grown without soil in artificial atmospheres, fed with chemical solutions and covered with thermal blankets. The result is predictable-quality, higher yields, shortened growing times and maximized profitability.
The industry is continually striving to reduce costs and quickly implements new techniques and products that increase efficiency. It is interesting to note that in such a scientifically dynamic and eager market, no new technology or product for the chemical feed of greenhouse crops has been introduced in many years. All major fertilizer companies make virtually the same non-innovative 25-pound bags of dry, granulated fertilizer.
Since the professional grower employs sophisticated water and fertilization equipment, he requires specialized premium-quality fertilizers. The most important property of premium fertilizer is that it dissolve completely in water and that the resultant solution is particle-free. The purpose of these seemingly simple but extremely important requirements is that the grower prepares a concentrate nutrient solution to be added to precise amounts to the watering system. This is done by means of a proportioner which injects enough fertilizer to make 100-400 parts per million dilution.
Not only is the proportioning meter sensitive, but the delivery system employs hypodermic syringe-like tubes which are easily clogged by insoluble matter. Clogging subsequently requires costly and time-consuming cleaning. The grower cannot afford to jeopardize his crops to equipment downtime and accordingly pay a premium for high-quality products (i.e., high solubility and, therefore, high availability of nutrients to the plant).
In general, the process of the invention utilizes the waste products of agricultural oil refining to create fertilizers for sale to agronomic and horticultural markets. The process views acid water as a resource recovery opportunity rather than a waste disposal problem. By employing xe2x80x9cnutrientxe2x80x9d chemicals, waste products which reduce margins become by-products that generate revenues and profits. The process is cost effective, utilizes standard equipment, permits compliance with the strictest effluent regulations, permits fatty acids to be recovered for full value on site, soapstock to be acidulated on-site rather than sold to acidulators below market values, offers the most ecologically desirable approach to managing process waste and presents the opportunity to refiners to employ the first closed-loop agricultural process system.
The simplest example of this philosophy is to replace sodium hydroxide with ammonia for the neutralization of acid water. Not only is there a substantial savings in chemical costs realize but, importantly, the compounds formedxe2x80x94ammonium sulfates and ammonium phosphatesxe2x80x94are salable fertilizers. The acid water can be so treated as to retain residual growth hormone from the vegetables, residual pesticides, surfactants and other ingredients which enhance its fertilizing capabilities.
Fertilizers for sale to the premium horticultural market can be produced by making additional changes. Substituting potassium hydroxide for sodium hydroxide in the refining step; acidulating the potassium soapstock with a combination of sulfuric and phosphoric acids in a prescribed manner; and then neutralizing the acid water with ammonia or potassium hydroxide will produce a multinutrient fertilizer containing N, P, K and S as well as desirable trace element micronutrients.
In either case the production of fertilizers for sale is both more cost effective and ecologically desirable than the disposition of a waste product.
Soapstock does not have to be treated with any H3PO4 to make fertilizer. The H3PO4 can be added after the soapstock is acidulated with H2SO4 or not at all. There is PO4-3 (from naturally occurring gums) already in the acid H2O and if additional PO4-3 needs to be supplemented, it can be done with H3PO4 (which, unless otherwise indicated, needs to subsequently neutralized with base). Or the acid water, before or after neutralization, can be supplemented with phosphate by addition of phosphate compound, salt, like MAP, DAP-MONO or di-ammonium phosphate.
The way to xe2x80x9cbestxe2x80x9d make fertilizer from the oil refining process may then be to:
1. Refine crude oil with potassium base (KOH), (other K salts may potentially be used).
2. Acidulate potassium soapstock with sulfuric acid (H2SO4).
3. Separate acid water form acid oil. At this point, the acid water contains; N (from gums) in a small %
P2O5-(from phosphatides)
K (from soapstock refinate)
S (from H2SO4 acidulation)
4. The acid water can be neutralized with a nitrogen base if desired (makes the best economic sense) like ammonia NH3, aqua (NH4OH) or with KOH if a specialty product is to be made (horticultural fertilizer).
Supplemental N or P can be added via MAP/DAP- or NH4NO3xe2x80x94 urea or not at all. If urea is used, better stability can be achieved by adding it later in the neutralization step.
The acid water from the potassium soapstock, acidulated with H2SO4, and neutralized with NH3, can be used as is (as a liquid) or concentrated by evaporation (still as a liquid); or concentrated far enough to cause crystallization of salts and continuously removing them.
Depending upon the phosphatide content of the crude oil (non-degummed oils are preferred) and the chemicals and techniques used in refining, the concentration of salts in the xe2x80x9cneutralized acid waterxe2x80x9d is approximately 20%.
Since it is desirable to produce a high analysis product, the dilute fertilizer solution should be concentrated. This can be accomplished by evaporation of water by natural or mechanical means, or by addition of material to upgrade the analysis.
If market demand require that a slurry or solid product be produced, crystallization techniques can be employed to make a variety of products.
Examination of the neutralized acid water will show a solution of multinutrient fertilizer: nitrogen from hydrolyzed phosphatides and ammonia; phosphorus (P2O5) from gums and phosphoric acid process additions; potassium (K2O) from the refining caustic; and sulfur (as sulfate) from the sulfuric acid acidulation. In addition, naturally occurring trace elements from the oilseed are present in free or chelated form.
Virtually everything present in this solution is beneficial to plant growth as, in fact, it is derived from plant seed material. This process can be considered to be a true closed-loop agricultural process system. What the plant removes from the soil is concentrated in the seed, removed during oil refining and replaced into the soil for the next crop cycle.
The fertilizer solution can be used as a liquid or crystallized to a solid.
Several crystal forms are possible, but the predominant salt is a potassium, ammoniumxe2x80x94phosphate, sulfate.
Many process variables are possible in order to tailor the final fertilizer preparation. One unique approach is to acidulate the potassium soapstock with sulfuric acid to a first pH below 7 and then complete the acidulation with phosphoric acid. By performing the acidulation in this manner all the phosphate added is found in the water phase, where it is wanted, without expensive losses in the oil phase. This procedure permits the relative percentages of sulfur and phosphorus to be varied considerably.
In another aspect of the invention, it may be preferable to use Ca(OH)2 as a nutrient neutralizer of acid water to produce calcium phosphate for use as a feed supplement to animals (i.e., an animal fertilizer).
It may be preferable to refine crude oil with Ca(OH)2 in order to have the Ca in the acid water.
Another aspect of the invention is the simple replacement of conventional sodium hydroxide with potassium hydroxide as the refining caustic. In the process of exploring the technical aspects of replacing the normal sodium hydroxide with potassium hydroxide in the process of caustic refining of crude agricultural oil, a number of important benefits have been discovered.
1. Less wash water.
One of the significant environmental deficiencies of conventional sodium hydroxide refining is that the refined oil which exits the centrifuge or separator must be processed through a number of water wash unit operations in order to remove any water soluble components from the refined oil. These water wash steps, in which water is mixed into the oil and then separated from the oil, produce a waste water stream with extremely low levels of water soluble components. It has been found that the refined oil product of potassium hydroxide refining can be brought to a given level of purity of water soluble components using less volume of water than would be true of the product of sodium hydroxide refining. This lower volume of waste water for a given level of oil purity reduces the waste water disposal problems both in terms of cost and environmental impact. In a refinery with a fixed number of wash stations, less volume of water can be used in each wash station. Conversely, in a new refinery design to take advantage of this aspect of potassium hydroxide refining, fewer wash stations and the commensurate savings and equipment cost, could be realized.
2. Higher clarity of oil.
It has been found that the oil which is the product of the potassium hydroxide refining process has a higher degree of clarity than oil produced using sodium hydroxide refining. Because the clarity is a major factor in the consumer acceptance of the refined oil, and therefore significantly impacts on the value of the oil product, this clarity feature, though primarily cosmetic, does significantly add to the value of the product.
3. More oil recovered.
It has been found that the use of potassium hydroxide in the refining process causes the recovery of a larger amount of refined oil from a given amount of crude oil. Thus, the productivity of the refining process, based on a given amount of crude oil input is increased and therefore the economics of the refining process is improved.
4. Reduced oil loss.
It has been found that the use of potassium hydroxide in the cost refining process reduces the amount of oil which is contained in the centrifuge or separator waste stream known as soapstock. Since the volume of soapstock generated by the refining of a given amount of crude oil is essentially considered a waste product having low value (or in fact frequently a net deposal cost), the ability to reduce the volume of soapstock by reducing the amount of oil contained in it is a significant economic and environmental benefit to the choice of potassium hydroxide as the refining caustic.
5. More interlayer removed.
One of the complicating components of the caustic refining process is the so-called interlayer or gum. This interlayer primarily consists of complex organic molecules including phosphorites. The amount of this interlayer which is formed in the potassium hydroxide version of caustic refining is significantly less than the amount that would be formed using sodium hydroxide refining. Because this interlayer component creates significant purification problems generally referred to as xe2x80x9cdegummingxe2x80x9d and because the amount of the interlayer tends to reduce the amount and purity of the desired refined oil, the fact that the amount of interlayer formed in potassium hydroxide refining is less not only improves the economics of the refining process but also simplifies the process and the disposal problems caused by it.
6. Increased soap in soapstock.
Because the use of potassium hydroxide in the caustic refining step appears to allow a more effective separation of the refined oil from the soapstock, there appears to be a greater amount of soap that actually ends up in the soapstock stream. Because the values of the soap itself can be much more readily realized when it is part of the soapstock stream, as opposed to representing trace impurities in the refined oil stream, this improved separation improves the economics of the overall process.
7. Potassium soapstock is less viscous.
The soapstock which is produced by the use of potassium hydroxide in the caustic refining process, has been found to be significantly less viscous, at a given concentration, then the soapstock produced using sodium hydroxide refining. This reduced viscosity of the potassium soapstock makes the potassium soapstock very significantly easier to handle and transport between the refining process operation and the acidulation process operation. This ease of handling would be a benefit to the process even if the refining-acidulation processing were integrated. In fact, however, the industry has developed in such a way that the refining activities and the acidulation activities are normally conducted significant distances apart. As a result, it is normally necessary to load the soapstock into railroad tank cars, tank trucks, or barges in order to move the soapstock from the refinery to the acidulation facility. The ease of handling the less viscous potassium soapstock is of significant benefit in simplifying and reducing the cost of this transport operation.